When I first mentioned that I wrote this, it was suggested that I publish it.  So... here it is:

http://www.industrial.mu/tools/php2relay.txt

Basically, it's a quick and dirty open SMTP relay tester that will work on a range of IP addresses.  Yes, it's written in PHP, and you'll need PHP5.  (I suck at teh Perl, so... deal )

Just copy it, save it, run it with> php php2relay.php (options)
Or make it executable, and drop the initial php.  Should process either way. 

Also, verify your php binary with "which php" and modify the first line as necessary.

Have fun, use responsibly, let me know if there are any questions.

Well, hope it helps!  Let me know how it turns out for ya...